1. Field
The present disclosure relates generally to position or location estimations of mobile communication devices and, more particularly, to techniques for a faster time-to-first-fix for use in or with mobile communication devices.
2. Information
Mobile communication devices, such as, for example, cellular telephones, portable navigation units, laptop computers, personal digital assistants, or the like are becoming more common every day. Certain mobile communication devices, such as, for example, location-aware cellular telephones, smart telephones, or the like may assist users in estimating their geographic locations by providing positioning assistance data obtained or gathered from various systems. For example, in an outdoor environment, certain mobile communication devices may obtain an estimate of their geographic location or so-called “position fix” by acquiring wireless signals from a satellite positioning system (SPS), such as the global positioning system (GPS) or other like Global Navigation Satellite Systems (GNSS), cellular base station, location beacon, etc. via a cellular telephone or other wireless communications network. In some instances, acquired wireless signals may be processed by or at a mobile communication device, and its location may be estimated using known techniques, such as, for example, Advanced Forward Link Trilateration (AFLT), base station identification, or the like.
In an indoor environment, at times, certain mobile communication devices may be unable to reliably receive or acquire satellite or like wireless signals to facilitate or support one or more position estimation techniques. For example, signals from an SPS or other wireless transmitters may be attenuated or otherwise affected in some manner (e.g., insufficient, weak, fragmentary, blocked, etc.), which may at least partially preclude their use for position estimations. As such, in an indoor environment, different techniques may be employed to enable navigation or location services. For example, a mobile communication device may obtain a position fix by measuring ranges to three or more terrestrial wireless access points positioned at known locations. Ranges may be measured, for example, by obtaining a Media Access Control identifier (MAC ID) address from wireless signals received from suitable access points and measuring one or more characteristics of received signals, such as signal strength, round trip delay, or the like.
At times, an indoor location of a mobile communication device may be estimated via radio heat map signature matching, for example, in which current or live characteristics or signatures of wireless signals received at the device are compared with expected or previously measured signal characteristics stored as heat map values in a database. For example, during an off-line stage, a particular indoor area may be surveyed, and heat map values, such as in the form of observed characteristics of wireless signals indicative of received signal strength (e.g., RSSI, etc.), round-trip delay times (e.g., RTT, etc.), or the like may be collected or compiled. During an on-line stage, a mobile communication device may utilize heat map values, such as stored in a local memory or provided to the device (e.g., for a download, etc.) via a local server, for example, for matching against current or live signal signatures. By finding a signature in a database that more closely matches characteristics exhibited by signals currently received at a mobile communication device, a location associated with a matching signature may be used as an estimated location of the device.
In some instances, however, such as in larger indoor or like areas with multiple access points or feasible routes, for example, a radio heat map may be quite voluminous or comprehensive so as to tax available bandwidth in wireless communication links, memory of a mobile communication device, or the like. In addition, downloading or otherwise accessing voluminous or comprehensive radio heat maps may, for example, lead to longer latencies with respect to initial position estimations. This may also increase power consumption of certain mobile communication devices, such as mobile devices with limited power resources (e.g., battery-operated, etc.), for example, thus, affecting operating lifetime or overall utility of such devices.